Tuesday, December 31, 2013

Sprit Rig Virtues and Details

Of my published designs, two of the most popular (Phoenix III and First Mate) make use of a sprit rig with a small jib set flying. You can read some of my comments about the rig in this post from May 2012.

Phoenix III showing-off her sprit rig and flying jib
Despite the simplicity and effectiveness of this rig, I receive a large number of enquiries about the details of setting and reefing, and it appears to me that many people are unsure of how to benefit from its virtues. This is a real pity, because the sprit rig can set a very large sail area from a very short mast, and is a rig which is ideally suited to small boat cruising. In addition, if set properly, it is a good sail for windward work.

Phoenix III tacking away from a Pooduck Skiff in a battle to get up-wind
For me, one of the great joys associated with small craft is experimentation with rig variations, and learning how to make rigs which use an absolute minimum of store-bought fittings. There are plenty of old books about traditional seamanship around, and time spent learning is a good investment.

Below is an except from Phil Bolger's book, 100 Small Boat Rigs (Copyright 1984 International Marine Publishing ISBN 0-87742-182-X)

Back to the 17th century. What I've said about spritsails in Rig 23 ap­plies. By adding a jib to the basic boomless spritsail, some extra area is added in an efficient form, without any multiplication or lengthening of the few short spars. The jib is a good airfoil in its own right, and the draft off it improves the drive of the mainsail. The position of the jib is perfect for a leading-edge device. The spritsail is prone to twist on ac­count of the difficulty of keeping the peak up tight. But the jib compen­sates for the twist to some extent. Taking the jib off doesn't affect the balance of the rig as much as might be thought. If it's sheeted correctly, 10 or 12 degrees out from the centerline, the pull of the sheet tends to swing the bow into the wind. The forward position of the sail has a sur­prisingly small tendency to knock her bow off the wind. By the same token, if you want to make a boat weathercock downwind, as in a broken-down powerboat that won't steer if she gets broadside to the wind, a loose-footed staysail is not the best sail to make her do it.

This is one of the few sloop rigs that can be weatherly without backstays or standing rigging of any sort. The spritsail's mast is so short that it can be built very stiff without its weight overpowering the boat. With the sloop rig the mast is stepped farther aft than in a cat, so the weight of a heavy mast does still less harm.

Moreover, the head of a spritsail is in tension, even when it isn't set up as hard as it should be, and that holds the masthead. The peak halyard of a gaff sail has the same effect, but it's not as powerful because there's less trouble keeping a gaff sail properly peaked: the angle of the halyard to the top of the taller mast of the gaff sail works at a better mechanical advantage. The halyard is also slipping on a sheave, with the vector of its force dividing the angle of the standing part and the fall, while the throat of a spritsail can be lashed, or even shackled, solidly in place.

Of course any cantilevered mast has some give. A big boat with this rig would need something by way of a backstay to get the most drive out of the close-hauled jib. In the 15-footer cartooned, with a 13 1/2-foot mast and sprit, and a jib of 18 square feet, the backstay isn't crucial. The rig is auxiliary to the oars, and since it is a spritsail, the spars can not only be stowed in the boat, but stowed out to the sides to be out of the way of the oarsmen. This is the most powerful and weatherly rig that can meet that specification. The fact that it's a cheap rig, easily built, strong and reliable, easy to maintain, and readily repaired with makeshift material, is an incidental bonus.

For those of you who would like to learn more about the rigging and versatility of a spritsail, there are three exceptionally good illustrated articles available in back issues of Woodenboat Magazine  #89 and #165.  The magazines are available as instant digital downloads for only a few dollars each, and I recommend them to you. Here are links to both issues: -

Sunday, December 22, 2013

Phoenix III in Woodenboat Magazine

In late September this year, I was approached by Woodenboat Publications to see whether I would be prepared to write a "How to Build" article about Phoenix III. I was delighted to be given the opportunity, but the catch was that the manuscript, photos, and drawings had to be submitted in two weeks.

Dan Taylor's home-built Phoenix III sailing in the Pacific North-West USA
(photo courtesy Dan Taylor and Nik Warden)
The writing didn't worry me too much, as I had plenty of material on hand. My major concern was that the plans for Phoenix III represented my very first attempt at using CAD as my drawing medium, and I had to teach myself as I went along. The program used was AutoSketch (from AutoDESK - the makers of AutoCAD) which is a very simple 2D product I use to this very day. Rather than relying on a sophisticated computer program to automatically produce drawings from 3D modelling, I determine the shape of my designs using a variety of methods - from carving a half-model to 3D modelling in DELFTship Professional. Once I have a three-dimensional shape which satisfies me, regardless of the method used, I take dimensions and draw the final CAD plans one line at a time in exactly the same way as I would on a drawing-board - it is just that I use a mouse instead of a pencil, and a screen instead of paper.

The original half-model which provided the starting point for the design

Drawing the lines of Phoenix III a long time ago.
I was not satisfied with the presentation of my early CAD drawings and had for a long time intended to re-draft the Phoenix III plans - not to alter the shape of the boat - just to make the plans more professional. The opportunity provided by the editors of Woodenboat left me little choice, as they wanted a complete set of building plans to accompany the three-part article, and I needed to consolidate the drawings from the previous 30-sheet (A3-sized) presentation to a smaller number of sheets, but making sure that the text and dimensions on the A1-sized sheets would be readable when reduced to the size of a magazine page.

The redrafting process took me about nine or ten days of intense effort, with most days starting early in the morning and running through until about 11pm. After that, I wrote and/or re-edited 16,500 words of text in four days!

One of the new plan sheets
In the same manner as previously, I offer plans in either metric or imperial editions, and they are available in an A3 comb-bound format or as A1 rolled sheets at a substantially higher price due to the printing and postal costs. In both instances, the plans are identical except for the scale of the drawings, with the A3 edition being the standard. As soon as I have a new website published, I will also be offering pdf download editions.

The first part of the three-part article is now on the market in Woodenboat number 236  . You will be able to build the boat directly from the magazine if you wish - all you need to do is to purchase Woodenboat issues number 236, 237, and 238. Certain items will be missing, such as full-sized patterns for side deck hanging knees, boom jaws and oarlock blocks, but the information required to determine their shape is provided. However, the editors (and I) recommend the purchase of a full set of plans if you are serious about building.

Here is a link to a low-resolution video clip of Phoenix III sailing in light conditions, viewed from outside the hull. Despite the low image quality, the clip is worth viewing in order to see how the easily-driven, lean hull slices through the water. Video courtesy of Rick Sutton and Paul Hernes